1. Field of the Invention
The present invention relates to an image processing system in which, when a plurality of images are composed, one of the images is transformed in order to facilitate a position-matching operation of the images.
2. Description of the Related Art
Conventionally, an image composition technique is known, such as HDR (i.e., high dynamic range imaging), by which a dark area and a bright area contained in the same image are clearly indicated. An image-blur correcting composition method is also known as an image composition technique, by which an influence of camera-shake is reduced. In HDR, an average image is created from an image captured at a higher shutter speed and an image captured at a lower shutter speed, so that an image having a virtually wide dynamic range is obtained. In the image-blur correcting composition method, a plurality of images are captured at a high shutter speed, such that the camera shake will hardly affect the images, and then summed together so that a single image, in which an influence of camera-shake is reduced and which has sufficient brightness, is obtained. Thus, various image composition techniques using a plurality of images have been proposed.
In image compositions using a plurality of images, it is required that pixels positioned at the same coordinates in the images correspond to the same point of the object. However, in a plurality of images, which are photographed without a tripod at a different time, a small deviation may occur in the images because of a translation or rotation of the camera.
Thus, some methods for position-matching two images have been proposed as disclosed in US2008/0175439 (A1). In '439, motion vectors of a plurality of target blocks, set in one image, are calculated for the target blocks, and the magnitude of translation and the rotational angle about the optical axis of the whole image are calculated based on the motion vectors.
According to the method disclosed in '439, an image composition using a position-matching operation can be performed between two images for a translation and a rotation about the optical axis. However, when a camera is rotated about an axis perpendicular to the optical axis (e.g., panning or tilting), it is difficult to compose images using a position-matching operation because the object images contained in the two images are deformed.